The printing image is formed when the print heads jet ink to the media. Observers can see the specific color when one or multiple kinds of ink drop on the media such as yellow, cyan, magenta, black, etc. This requires the image to be printed on the white media or similar white media to make sure the color finally printed is correctly seen by the observers. Or else, the image seen by the observers will be influenced by the background color shielded by printing image.
Therefore, before printing color image on the non-white media (such as color media or transparent media), white ink should be printed on the media as background. For example, to print a color image on the black or color media, we need to print white ink in the field where color image will be printed first, and then print color image shielding the white ink layer. The base color white protects the color image from being influenced by the base color of the black media or color media.
To print on the transparent media, you need to print color ink on the transparent media first and then print white ink shielding color ink. Then you can observe the color printing image through transparent media in the front of the said media, which is called the foreground color printing mode. The white ink layer can be served as the background of color image so that the color observed from the front of transparent media is normally displayed.
To print double images on the transparent media, you need to print the first color image on the transparent media and then print the first white ink layer shielding the first color image. If the second color image is the same with the first color image, you can directly print the second color image on the first white ink layer. Since the white ink can transmit light, the first color image layer may be mixed with the second color image layer. Therefore, if the second color image is different from the first color image, we need to print a gray ink layer on the first white ink layer. The second color image will be abnormally displayed if it is printed directly on the gray ink layer, so the second white ink layer should be printed on gray ink layer before printing the second color image. This not only ensures the saturation and verisimilitude, but also avoids the mixture of the first color image layer and second color image layer. In conclusion, five layers of ink should be printed if we want to print double layers color image on transparent media. The inkjet printing apparatus and printing method need to be provided for five layers printing through media one-transport.